Three phase motors are widely used for industrial service because three phase power can be generated and distributed more economically in large quantities than single phase power. A three phase induction motor includes a stator containing a stator winding and a rotor containing a rotor winding. The operation of three phase induction motors depends on a rotating magnetic field in the air gap between the stator, or stationary part, and the rotor, or rotating part, of the motor. The rotating magnetic field causes rotation of the rotor at nearly the frequency of the power source. The rotor of a so-called squirrel cage motor has a laminated iron core with slots on its periphery. Uninsulated conductors are imbedded in the slots of the cylindrical rotor core and are connected to each other at each end of the rotor. The squirrel cage motor is the most widely used motor of any type because of its rugged simplicity and low cost. It is used to drive such loads as fans, blowers, machines, centrifugal pumps and motor-generator sets. A polyphase induction motor is simple in the sense that the rotor is the only moving part and electrical connections to the rotor are not required. In addition, polyphase induction motors operate with high efficiency at, or near, full load.
Because most homes and rural areas are provided only with single phase power, polyphase induction motors are not used in home appliances. In addition, polyphase induction motors have two major disadvantages. When lightly loaded, they have much lower efficiencies than when fully loaded. Furthermore, the motor speed is determined by the power source frequency and the number of poles in the stator winding, thereby making variable speed operation difficult. Variable speed operation of induction motors has been achieved by a number of techniques. Multiple windings provide a number of pole configurations and a number of discrete operating speeds. The voltage of the stator supply can be varied to provide some speed variation. However, efficiency is reduced at low speeds. The frequency of the stator supply can be varied. However, this results in a substantial increase in cost, since a variable frequency supply of even moderate output power is expensive. Wound rotor induction motors with slip rings permit speed to be varied by varying the rotor resistance, and slip control techniques have been utilized. Any of these techniques add to the cost of the motor substantially and are often limited in effectiveness.
Polyphase induction motors were invented by Nikola Tesla a hundred years ago and, by now, represent a mature technology. Modern motors are virtually unchanged except for design improvements.
It is a general object of the present invention to provide a novel polyphase induction motor system.
It is another object of the present invention to provide an induction motor system incorporating a real-time computer to control and switch system parameters.
It is another object of the present invention to provide a new and improved induction motor system using a real-time microcomputer to dynamically and programmably switch components of the stator winding.
It is another object of the present invention to provide an inexpensive and controllable source of mechanical power from an electric power source.
It is another object of the present invention to provide an induction motor system including an integral microprocessor for control of operating characteristics.
It is another object of the present invention to provide an induction motor system with variable speed obtained by computer control of the stator winding configuration, the stator supply frequency and the number of phases in the stator power supply.
It is another object of the present invention to provide an induction motor system having dynamically controlled starting regimes without elaborate switchgear or special rotor windings.
It is another object of the present invention to provide an induction motor system having controlled acceleration to a preselected speed without drawing excessive starting current.
It is another object of the present invention to provide an induction motor system wherein the motor may be instantaneously tuned to the load by selectively energizing only part of the stator winding.
It is another object of the present invention to provide an induction motor system in which undesirable effects due to harmonics and other causes are minimized by supplying each conductor with in-phase energy whose power distribution is such as to suppress or eliminate said undesirable harmonics.
It is another object of the present invention to provide an induction motor system with smooth dynamic braking by progressively diminishing the rotary speed of the stator magnetic field so that the rotor overruns it.
It is another object of the present invention to provide an induction motor system in which the speed, torque and power output can, jointly or individually, be dynamically altered according to one or more protocols programmed into the integral controller.
It is another object of the present invention to provide an induction motor system in which the speed, torque and power output can, jointly or individually, be dynamically altered by an external control system or computer interfaced to and interacting with programs embodied in the integral motor control circuitry.
It is another object of the present invention to provide a variable speed polyphase induction motor system which can operate from a single phase supply with the efficiency of a polyphase motor matched to its optimum load.
It is another object of the present invention to provide an induction motor system that will run smoothly at all operating speeds, accelerating or decelerating smoothly when the speed needs changing.
It is another object of the present invention to provide an induction motor system having simultaneous high efficiency, variable speed and easy starting characteristics.